The long-term goal of this project is to develop a therapeutic human papillomavirus (HPV) vaccine that would prevent cervical cancer and other cancers caused by high-risk HPV types in individuals already infected, at which point currently available HPV prophylactic vaccines are not effective. This competitive renewal application proposes to conduct a Phase II clinical trial treating women with biopsy-proven high-grade squamous intraepithelial lesions (HSILs). HSILs are precursors of cervical cancer, which is almost always caused by HPV and is the fourth most common cancer among women worldwide, with annual incidence of 528,000 cases and mortality of 266,000 cases. In addition, HPV causes anal, oropharyngeal, penile, vaginal, and vulvar cancers; it is estimated that HPV is responsible for 5.2% of the cancer burden. Standard surgical treatments for HSILs are effective but have the unintended consequence of doubling the rate of preterm delivery afterward. Therefore, an alternative, such as a therapeutic HPV vaccine, is needed that would work by stimulating cell-mediated immunity without compromising cervical anatomy. Our group is developing an HPV therapeutic vaccine - PepCan - that consists of four current good manufacturing grade synthetic peptides that cover the E6 protein of HPV type 16 (HPV 16), along with a Candida skin-test reagent as a novel vaccine adjuvant. The immune response to the E6 protein has been associated with good clinical outcomes in naturally HPV-infected women with and without cervical lesions, and Candida injection has been shown to regress common warts and induce T-cell responses. The ongoing Phase I clinical trial has demonstrated safety, immunological responses, and histological regression above that of a historical placebo control. The proposed Phase II study will assess efficacy by extending the observation period from 3 months (in Phase I) to 1 year, which is the length of time required for similar therapeutic vaccines to take full effect. As efficacy was demonstrated against HSILs associated and not associated with HPV 16, a Candida treatment arm will be added in a randomized, double-blinded fashion. The additional goals are to identify factors associated with vaccine response, examine vaccine effect, and define the other HPVs that can be treated with PepCan. We hypothesize that PepCan induces HSIL regression and HPV clearance by mounting immune responses with measurable signatures against multiple HPV types. This hypothesis will be tested with the following aims: Aim 1: assess efficacy and safety of our HPV therapeutic vaccine in a Phase II clinical trial; Aim 2: identify factors associated with a favorable vaccine response, and examine the effects of vaccination; and Aim 3: describe non-HPV 16 types against which this vaccine is effective. Epitope spreading, cross-reactivity of T cells, and de novo immune stimulation will be investigated as possible mechanisms of cross-protection. Successful completion of this project should lead not only to an FDA-approved HPV therapeutic vaccine for cervical cancer but also to a new modality for prevention and treatment of all cancers caused by HPV.